Multivalent Proteins Rapidly and Reversibly Phase-Separate upon Osmotic Cell Volume Change

Area of Science:

• Cell Biology
• Biochemistry
• Molecular Biology

Background:

• Subcellular, membraneless compartments like processing bodies (PBs) and stress granules (SGs) form under physiological and stress conditions.
• The dynamic assembly and disassembly of these compartments are crucial for cellular responses.

Purpose of the Study:

• To investigate the rapid phase separation of proteins in response to hyperosmotic stress.
• To elucidate the mechanism and scope of this stress-induced cellular response.

Main Methods:

• Observation of trimeric PB protein DCP1A phase separation in mammalian cells using live-cell imaging.
• Correlation analysis between phase separation, cell volume compression, and stress granule assembly.
• Assessment of the impact on transcription termination and sequestration of pre-mRNA cleavage factors.

Main Results:

• The protein DCP1A rapidly phase-separates within seconds during hyperosmotic stress and dissolves upon rescue.
• This rapid intracellular hyperosmotic phase separation (HOPS) is linked to cell volume compression and is distinct from stress granule assembly.
• HOPS broadly occurs in homo-multimeric proteins across various cell types and sequesters transcription-related factors, impairing transcription termination.

Conclusions:

• The multimeric proteome exhibits a rapid response to hydration and molecular crowding changes.
• Globally programmed phase separation and sequestration represent an unexpected cellular mechanism for responding to osmotic stress.
• This process provides a novel insight into the regulation of gene expression under stress conditions.